Silver halide peptizers



"ted States Patent 3,520,857 Patented July 21, 1970 US. Cl. 26080.3 3 Claims ABSTRACT OF THE DISCLOSURE Copolymers comprising at least about 40 to 100 mole percent of an acrylyl or methacryl histidine and up to about 60 mole percent of acrylic or methacrylic acid. In one aspect, polymers of this type are good peptizers for silver halide photographic emulsions.

This is a division of application Ser. No. 420,160, filed Dec. 21, 1964, and now US. Pat. No. 3,419,397.

This invention relates to silver halide dispersions, and more particularly to the method of preparing silver halide dispersions which features the use of certain polymeric peptizers.

The initial step in the preparation of a photographic emulsion is the precipitation of crystals of a silver halide (or a mixture of silver halides) into a peptizer which functions to prevent clumping or aggregation of the silver halide crystals. Clumping and aggregation result in inhomogeneities in the coated photographic product, excessive graininess and occurence of infectious development. An emulsion which is peptized to prevent clumping or aggregation of the silver halide crystals is said to be stabilized. To be a satisfactory peptizer, it is not only necessary that the peptizer function to stabilize the grains, but the peptizer must also allow the silver halide crystals precipitated therein to grow to a sufficiently large size to possess at least the required minimum photographic sensitivity. Most of this growth should occur by processes of ionic deposition of silver ions and of halide ions on the growing crystals. This type of growth results in grains of regular crystalline shape, and the sensitivity of crystals of this type lies predominantly on the surface rather than in the interior of the crystals. Most photographic applications prefer silver halide grains having a high ratio of sur face sensitivity to internal sensitivity.

Whil gelatin has previously been used as peptizer, it is well known that the use of gelatin involves a number of inherent disadvantages. As a naturally occurring material its composition may vary from time to time and, because of its natural origin, it is subject to attack by bacteria and molds. In addition, it would be desirable to obtain crystals differing significantly in photographic characteristics from the silver halide crystals which are obtained when gelatin is employed as peptizer.

Various polymers have previously been proposed as substitutes for gelatin as peptizers. However, many of the polymers previously proposed do not adequately stabilize the emulsion against clumping and aggregation of the crystals. An example of a polymer of this type is polyacrylamide. Other polymers, such as poly(vinyl alcohol) or poly(vinylpyrrolidone) are effective stabilizers for the emulsion grains, but exert a pronounced inhibiting effect on growth of the emulsion grains during physical ripening, i.e., treatment of the grains at elevated temperature to increase crystal growth. Such polymers are, of course, not entirely acceptable as peptizers for silver halide.

One object of our invention is to provide polymeric peptizers for silver halide dispersions. Another object of our invention is to provide a method for preparing silver halide dispersions which features the use of certain novel polymeric peptizers which result in silver halide crystals having photographically significant differences in crystal structure from the silver halide crystals which are obtained when gelatin is employed as peptizer. Other objects of our invention will appear herein.

These and other objects of our invention are accomplished by a method of preparing silver halide dispersions which comprises reacting a water soluble silver salt with a water soluble halide salt in an aqueous solution containing a polymer having 40 to 100 mole percent, and preferably 40 to mole percent, of the following reand 0 to 60 mole percent, and preferably 60 to 30 mole percent, of the following repeating unit:

g1 I{the above formulas R and R each represents CH or We have found that when silver halide is precipitated in the presence of the copolymers employed as peptizers in accordance with the invention, that the emulsion is well stabilized against clumping and aggregation of silver halide crystals, and that the copolymers do not restrain but rather promote silver halide crystal growth during the physical ripening of the emulsion. The silver halide crystals obtained differ significantly in photographic characteristics from silver halide crystals obtained when gelatin is employed as peptizer. Our invention will be further illustrated in the followlng examples. Examples 1 and 2 demonstrate that copolymers of N -methacrylylhistidine and acrylic acid contain mg no more than about 32 mole percent N -methacrylylhistidine are unsatisfactory peptizers for photographic emulsions, and Examples 3-9 demonstrate the highly useful results obtained when the copolymers of the invention are employed as peptizers.

EXAMPLE 1 A solution of 31 g. (0.20 mole) of L-histidine and 35 g. (0.22 mole) of methacrylic anhydride in 250 ml. of methacrylic acid was placed on a shaker for 18 hours. It was then poured into 3 l. of diethyl ether to precipitate the product, which was washed in fresh ether. The material was dried in air, redissolved in 200 ml. of ethanol, and reprecipitated in ether. Vacuum drying gave 40 g. of amorphous N -methacrylylhistidine.

Analysis.Calcd for C H N O (percent): N, 18.8. Found (percent): N, 18.9.

A solution of 11 g. (.050 mole) of N -methacrylylhistidine, 12 g. (0.17 mole) of acrylic acid and 0.20 g. of azodiisobutyronitrile in ml. of dioxane and 30 ml. of water was heated under nitrogen at 50 C. for 17 hours. The copolymer which separated was washed in several changes of water. The water-swollen copolymer was used for making photographic emulsions; a sample was dried for analysis which showed 11.2% nitrogen corresponding to 32 mole percent methacrylylhistidine.

An emulsion of the type known to those skilled in the art as a neutral emulsion was prepared in accordance with the following procedure. A silver nitrate solution was prepared which contained 3.82 g. of silver nitrate in ml. of aqueous solution. This silver nitrate solution was subsequently added at a constant rate to ml. of a continuously stirred solution, which contained 3.275 g. of potassium bromide, 0.1 g. of potassium iodide and 1.0 g. (dry basis) of copoly(N-methacrylylhistidine-acrylic acid) containing 32 mole percent N"-methacrylylhistidine. The latter solution had previously been heated to 70 C. and this same temperature was maintained throughout the 30-minute period of silver nitrate addition as well as during 30 minutes of subsequent additional stirring of the emulsion. The emulsion obtained showed unsatisfactory stability as many grains were found to be in a clumped or aggregated state. Furthermore, in spite of continuous efficient stirring, a substantial fraction of the emulsion had sedimented to the bottom of the precipitation vessel.

EXAMPLE 2 An emulsion of the type known to those skilled in the art as an ammoniacal emulsion was prepared in accordance with the following procedure. A solution of silver nitrate was converted to a solution of the ammoniacal complex of silver nitrate by adding sufiicient ammonium hydroxide to 11.25 ml. of an aqueous solution containing 3.82 g. silver nitrate to just redissolve the precipitate which had formed initially on addition of ammonium hydroxide to the silver nitrate solution. The volume of the solution was then brought up to 20 ml. with water. The ammoniacal silver nitrate solution obtained in this manner was then added at constant rate over a period of 85 seconds to a continuously stirred solution containing 3.14 g. of potassium bromide, 0.1 g. of potassium iodide and 1.0 g. of copoly(N"-methacrylylhistidine-acrylic acid) containing 32 mole percent N"-methacrylylhistidine, described in Example 1. The temperature of the solution containing the potassium bromide, potassium iodide and the polymeric peptizer had been brought to C. prior to addition of the silver nitrate. The temperature of the emulsion was held at 45 C. throughout the addition of the silver nitrate solution as well as during 39 minutes of additional continuous stirring after all the silver nitrate had been added. The emulsion obtained was characterized by unsatisfactory stability as a considerable number of emulsion grains were found to be clumped or aggregated.

EXAMPLE 3 A copolymer from 9.0 g. (.041 mole) of N -methacrylylhistidine and 3.0 g. (.042 mole) of acrylic acid was made by heating the monomers with 0.12 g. of potassium persulfate under nitrogen in 40 ml. of water at 60 for 3.5 hours. The polymer was washed with water and used without drying. A nitrogen content of 19.1% in a dried sample indicated 44 mole percent N-methacrylylhistidine.

A neutral emulsion was prepared as described in Example 1 except that the peptizer used to prepare this emulsion was copoly(N methacrylylhistidine acrylic acid) containing 44 mole percent N -methacrylylhistidine. The resulting emulsion showed excellent stability and was free from any undesirable clumping or aggregation elfects. The grains constituting this emulsion were tabular octahedral crystals with diameters within the range 0.5-4.0 microns. The average grain size diameter was 1.30 microns.

EXAMPLE 4 An emulsion of the type known to those skilled in the art as a neutral emulsion was prepared in the following manner. An aqueous solution with volume equal to 20.0 ml. and containing 1.954 g. silver nitrate was added at constant rate over a period of 20 minutes to 30 ml. of a continuously stirred solution containing 1.67 g. of potassium bromide, 0.051 g. of potassium iodide and 1.0 g. of copoly(N -methacrylylhistidine-acrylic acid) containing 44 mole percent N-methacrylylhistidine, described in Example 3. The temperature of this solution containing potassium bromide, potassium iodide and peptizer had been raised to 60 C. prior to addition of the silver nitrate. The temperature of the emulsion was held at 60 C. throughout the period of silver nitrate addition as well as during an additional 20-minute period of continuous stirring following completion of silver nitrate addition as well as during an additional 20-minute period of continuous stirring following completion of silver nitrate addition. The emulsion obtained showed excellent stability and was free from any undesirable clumping, aggregation or sedimentation effects. The emulsion consisted of tabular octahedral grains with diameters within the range 0.4-1.9 microns. The average grain diameter was 1.01 microns.

EXAMPLE 5 An ammoniacal emulsion was prepared as described in Example 2 except that the peptizer used to prepare this emulsion was copoly(N methacrylylhistidine acrylic acid) containing 44 mole percent N-methacrylylhistidine, described in Example 3. The emulsion obtained showed excellent stability and was free from any undesirable clumping, aggregation or sedimentation effects. The grains of this emulsion were either cubic crystals or twinned-cubic crystals with diameters within the range 0.6-3.3 microns. The average grain diameter was 1.14 microns.

EXAMPLE 6 A solution of 13 g. (.058 mole) of N-methacrylylhistidine, 4.2 g. (.058 mole) of acrylic acid, 0.20 g. of azodiisobutyronitrile 'in ml. of water and 50 ml. of dioxane was heated under nitrogen at for 7 hours. The washed copolymer which resulted was used for making photographic emulsions without drying. A dried sample contained 15.2% nitrogen indicating a methacrylylhistidine content of 58 mole percent.

A neutral emulsion was prepared as described in Example 1 except that the peptizer used to prepare this emulsion was copoly(N" methacrylylhistidine acrylic acid) containing 58 mole percent of N-methacrylylhistidine. The emulsion obtained showed excellent stability and was free from any undesirable clumping, aggregation or sedimentation efiects. The grains constituting this emulsion were tabular octahedral crystals.

EXAMPLE 7 An ammoniacal emulsion was prepared as described in 'Example 2 except that the peptizer used to prepare this emulsion was copoly(N methacrylylhistidine acrylic acid) containing 5 8 mole percent N-methacrylylhistidine, described in Example 6. The emulsion obtained showed excellent stability and was free from any undesirable clumping, aggregation or sedimentation effects. The grains constituting this emulsion were cubic or twinned-cubic crystals with diameters within the range 0.5-1.8 microns. The average grain diameter was equal to 0.80 microns.

EXAMPLE 8 A solution of 18.5 g. (.076 mole) of N"-methacrylylhistidine, 1.4 g. (.019 mole) of acrylic acid, and 0.20 g. of potassium persulfate in 80 ml. of water was heated at 60 under nitrogen for 23 hours. A small amount of scum was removed from the solution by filtration, and the filtrate was poured into methanol to precipitate the copolymer. The washed polymer was dried to 12 g. A nitrogen content of 16.0% indicated 63 mole percent N- methacrylylhistidine.

A neutral emulsion was prepared as described in Example 1 except that the peptizer used to prepare this emulsion was copoly(N" methacrylylhistidine acrylic acid) containing 63 mole percent N-methacrylylhistidine. The emulsion obtained showed excellent stability and was free from undesirable clumping, aggregation or sedimentation effects. The emulsion consisted of tabular octahedral grains with diameters within the range 0.4-3.9 microns. The average grain diameter was 1.19 microns.

EXAMPLE 9 An ammoniacal emulsion was prepared as described in Example 2 except that the peptizer used to prepare this emulsion was copo1y(N methacrylylhistidine acrylic acid) containing 63 mole percent N -methacrylylhistidine, described in Example '8. The emulsion obtained showed excellent stability and was free from any undesirable clumping, aggregation or sedimentation effects. The grains constituting this emulsion were cubic crystals or twinnedcubic crystals with diameters within the range 0.331.5 microns. The average grain diameter was 0.68 micron.

Although the examples demonstrate the use of copoly (N-methacrylylhistidine-acrylic acid) polymers, equally good results are obtained with closely related polymers such as those containing N-acrylylhistidine or methacrylic acid in place of, or with, N -methacrylylhistidine and acrylic acid. The concentration of the copolymers in the reaction solution in which a water soluble silver salt is reacted with a water soluble halide salt may vary over a relatively wide range, but preferably is from about 0.06 to 0.4 parts per part of the silver halide precipitated.

The invention has been described in detail with particular reference to preferred embodiments thereof but it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

We claim:

1. A polymer comprising at least about 40 to 100 mole percent of the following repeating unit:

and comprising up to about mole percent of the following repeating unit:

R2 l: C Liz-ll] C O O H and comprising from about 30 to about 60 mole percent of the following unit:

(II) R2 [-CHawherein R and R are each selected from the group consisting of a hydrogen atom and a methyl group.

References Cited UNITED STATES PATENTS 2,891,025 6/1959 Price 260-883 3,288,707 11/1966 Hurwitz et al 260-88.3 3,419,397 12/1968 Merrill et al. 96-114 HARRY WONG, JR.,

US. Cl. X.R.

Primary Examiner 

